Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process via cumene. This is a three-step process involving alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide, and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone.
Another process involves the hydroalkylation of benzene to produce cyclohexylbenzene, followed by the oxidation of the cyclohexylbenzene (CHB) to cyclohexylbenzene hydroperoxide (CHBHP), which is then cleaved to produce phenol and cyclohexanone in substantially equimolar amounts. Such a process is described in, for example, U.S. Pat. No. 6,037,513, in which the hydroalkylation catalyst is a bifunctional catalyst comprising at least one hydrogenation metal and a molecular sieve of the MCM-22 family.
The oxidation of CHB is a gas-liquid reaction involving mass transfer of oxygen from the feed gas (e.g., air) into the liquid CHB where it reacts to form the CHBHP. In this reaction, sufficient distribution of dissolved oxygen is important to achieving the desired CHB conversion rate and selectivity to CHBHP. That said, one challenge is that the dissolved oxygen distribution cannot be effectively measured in existing liquid phase oxidation reactors.
Gas phase oxygen detectors are known and can be used to provide information about the overall consumption rate of oxygen, which implicitly describes the general effectiveness of the reactor performance. However, this technique does not provide information about the distribution of dissolved oxygen in the CHB. Furthermore, maintenance of online analytical equipment can be costly and requires regular upkeep. Lower cost methods using offline measurement are desirable.
According to the invention, it has now been discovered that the dissolved oxygen distribution is directly correlated to a ratio β, which is a ratio of at least two byproducts produced during the oxidation reaction. More specifically, it has been found that the dissolved oxygen concentration affects the amount of certain byproducts produced during the oxidation reaction. For example, at low dissolved oxygen conditions, more of certain byproducts (e.g., 1-phenyl-1-hexaphenone) are produced. At stoichiometrically sufficient or excess oxygen conditions, more of certain other byproducts (e.g., 6-hydroperoxyhexaphenone and 6-hydroxyhexaphenone) are produced. As such, a ratio of byproducts can be used to directly determine, or as a proxy for determining, the dissolved oxygen concentration in a CHB oxidation reaction.